In recent years, electronic mails (hereinafter called “emails”) have been becoming more important as information transmission means and have come into widespread use. Further, there is a tendency that the total number of transmitted emails is increasing year after year as the use of emails has become widespread. There are a lot of transmitted emails that are unnecessary for receivers or emails that become unnecessary when a certain period has elapsed after the emails are transmitted or after receivers have viewed the emails. Receivers divide these transmitted emails into unnecessary emails and necessary emails and delete the unnecessary emails by using deletion settings in email software or on web-browsers. As an example of a method for deleting a received email, Patent Literature 1 discloses an email deletion reservation system. This email deletion reservation system is a certain email software or the like installed in a terminal possessed by a receiver, and includes deletion reservation setting means for associating a specific deletion reservation date/time with a certain email according to an input setting by the receiver, and email deletion means for comparing the present date/time with that deletion reservation date/time and deleting that specific email at the deletion reservation date/time.